Ion mobility spectrometers (IMS) use an ionization source to ionize molecules from a sample of interest to identify the molecules. Once the molecules are ionized, the IMS measures the time it takes the ions to reach a detector. This type of IMS is referred to as a time-of-flight IMS. The IMS can use the ion's time-of-flight to identify the molecule because different ions have different time-of-flights based on the ion's ion mobility.
An IMS can include a radioactive source or an electrical source to ionize the molecules. For example, an IMS may include a radioactive nickel 63 (63Ni) source to ionize molecules. IMSs with electrical sources ionize molecules by discharging an electrical current. While different voltages can be used, an electrical source's voltage typically is sufficiently high to cause the molecule to have a single positive or negative charge, although fragmentation and different mass to charges ratios are possible.